Method and apparatus for wireless communication using beam-forming in wireless communication system

ABSTRACT

A method of operating a wireless communication device including a plurality of antennas according to an exemplary embodiment of the present disclosure includes determining an antenna subset including at least one of the plurality of antennas, transmitting a sounding reference signal (SRS) switching signal to a base station through at least one antenna of the antenna subset, receiving a channel state information-reference signal (CSI-RS) transmitted using a first beam from the base station, selecting a precoding matrix indicator (PMI) based on the CSI-RS, transmitting the selected PMI to the base station, and receiving a signal transmitted from the base station through a second beam determined based on the SRS switching signal and the PMI.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. § 119to Korean Patent Application No. 10-2021-0003565, filed on Jan. 11,2021, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to wireless communication andmore particularly to wireless communication using beamforming techniquesbased on determining channel characteristics.

DISCUSSION OF RELATED ART

Beamforming may refer to a method of transmitting or receivingdirectional signals using a plurality of antennas. As an example, a basestation may transmit a downlink signal to a terminal using a beamformingmethod. To determine the beam to be formed, the base station may assumethat the radio channel between the uplink (terminal to base station) andthe downlink (base station to terminal) is reciprocal, that is, achannel reciprocity condition exists. In this case, the base station maytransmit the downlink signal using the beamforming method based on adownlink channel condition which is estimated from the uplink signalreceived from the terminal. However, due to various factors, the uplinkand downlink channels may differ, whereby this technique may result ininaccurate downlink channel information, leading to suboptimalbeamforming.

SUMMARY

The present disclosure provides a wireless communication method and awireless communication device for transmitting a “sounding referencesignal (SRS) switching signal” by utilizing techniques such as antennaselection or beam selection, to optimize downlink beam determination ofa base station.

In one aspect, a method of operating a wireless communication deviceincluding a plurality of antennas according to an exemplary embodimentof the present disclosure includes determining an antenna subsetincluding at least one of the plurality of antennas, transmitting an SRSswitching signal to a base station through at least one antenna of theantenna subset, receiving a channel state information-reference signal(CSI-RS) transmitted from the base station through a first beam,selecting a precoding matrix indicator (PMI) based on the CSI-RS,transmitting the selected PMI to the base station, and receiving asignal transmitted from the base station through a second beamdetermined based on the SRS switching signal and the PMI.

In another aspect, a wireless communication device according to anexemplary embodiment of the present disclosure includes a plurality ofantennas, a radio-frequency integrated circuit (RFIC) including aswitching network connected to a plurality of antennas, a switchingnetwork configured to transmit a SRS switching signal to a base stationthrough at least one antenna included in the antenna subset; and aprocessor configured to determine an antenna subset including at leastone of the plurality of antennas, select a PMI to be provided to thebase station based on a CSI-RS transmitted using a first beam from thebase station, and process a signal transmitted from the base stationusing a second beam determined based on the SRS switching signal and thePMI.

In still another aspect, a method of operating a base stationcommunicating with a wireless communication device including a pluralityof antennas according to an exemplary embodiment of the presentdisclosure includes receiving a SRS switching signal transmitted usingan antenna subset including at least one of the plurality of antennas,estimating uplink channel information based on the SRS switching signal,estimating downlink channel information based on the estimated uplinkchannel information, determining and forming a first beam based on theestimated downlink channel information. A CSI-RS is transmitted throughthe first beam, and a PMI is received from the wireless communicationdevice. A second beam is determined and formed based on the received SRSswitching signal and the received PMI, and a signal including data istransmitted through the second beam.

In yet another aspect, a method of operating a wireless communicationdevice including a plurality of antennas involves determining an antennasubset including at least two but less than all of the plurality ofantennas. An SRS switching signal including a sequence of SRSs istransmitted to a base station, where each of the SRSs is respectivelytransmitted through a different one of the at least two antennas of theantenna subset. A reference signal, transmitted through a first beamfrom the base station, is received, and a PMI is selected based on thereference signal. The selected PMI is transmitted to the base station. Asignal is thereafter received from the base station, which wastransmitted through a second beam determined based on the SRS switchingsignal and the PMI.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the inventive concept will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1A is a block diagram schematically illustrating a wirelesscommunication system according to an exemplary embodiment of the presentdisclosure, and FIG. 1B is a diagram for explaining a radio channelbetween a wireless communication device and a base station of FIG. 1A;

FIG. 2 is a flowchart illustrating a method of operating a wirelesscommunication device and a base station in a wireless communicationsystem according to an exemplary embodiment of the present disclosure;

FIGS. 3A and 3B are flowcharts illustrating respective examples of amethod of transmitting a sounding reference signal (SRS) switchingsignal according to exemplary embodiments of the present disclosure;

FIG. 4 is a flowchart illustrating an example of a method oftransmitting an SRS switching signal according to a sequential antennaselection method according to an exemplary embodiment of the presentdisclosure;

FIGS. 5A and 5B are flowcharts illustrating examples of a method oftransmitting an SRS switching signal according to an opportunisticantenna selection method according to exemplary embodiments of thepresent disclosure;

FIG. 6 is a flowchart illustrating an example of a method oftransmitting an SRS switching signal according to an antenna spatialcorrelation-based selection method according to an exemplary embodimentof the present disclosure;

FIGS. 7A, 7B and 7C are flowcharts illustrating examples of a method oftransmitting an SRS switching signal according to an antenna selectionmethod based on reinforcement learning according to exemplaryembodiments of the present disclosure;

FIG. 8 is a flowchart illustrating an example of a method of tracking afinal antenna subset according to an exemplary embodiment of the presentdisclosure;

FIGS. 9A and 9B are flowcharts illustrating examples of a method ofselecting a pre-coding matrix indicator (PMI) according to exemplaryembodiments of the present disclosure; and

FIGS. 10A, 10B and 10C are block diagrams illustrating structures of awireless communication device according to exemplary embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the inventive concept will be described indetail with reference to the accompanying drawings.

FIG. 1A is a block diagram schematically illustrating a wirelesscommunication system 10 according to an exemplary embodiment of thepresent disclosure, and FIG. 1B is a diagram for explaining a radiochannel between a wireless communication device 100 and a base station110 of FIG. 1A.

The wireless communication system 10 may refer to any system including awireless communication device 100 and a base station 110. For example,the wireless communication system 10 may be any one of a New Radio (NR)system, a 5th generation wireless (5G) system, a Long Term Evolution(LTE) system, an LTE-Advanced system, a Code Division Multiple (CDMA)system, a Global System for Mobile Communication (GSM) system, or aWireless Local Area Network (WLAN) system. In the case of a CDMA system,this may be implemented in various CDMA versions such as wideband CDMA(WCDMA), time division synchronization CDMA (TD-SCDMA), cdma2000, andthe like. Hereinafter, the wireless communication system 10 will bedescribed with reference mainly to a 5G system and/or an LTE system, butit will be understood that exemplary embodiments of the presentdisclosure are not limited thereto.

The wireless communication network of the wireless communication system10 may support multiple users to communicate by sharing availablenetwork resources. For example, in a wireless communication network,information may be provided with various multiple access methods such asCode Division Multiple Access (CDMA), Frequency Division Multiple Access(FDMA), Time Division Multiple Access (TDMA), Orthogonal FrequencyDivision Multiple Access (OFDMA), Single Carrier Frequency DivisionMultiple Access (SC-FDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA, and thelike.

A base station (BS) 110 may be part of the wireless communication system10. The BS 110 may typically be a fixed station communicating withmultiple user equipments (UEs), but in other examples, user equipmentcan be configured to function as a base station. The BS 110 maycommunicate with another BS 112, and may exchange data and controlinformation by communicating with a UE and/or other “cells” (e.g., otherBSs that each typically service a certain geographical area). Forexample, the BS may be referred to as a cell, a Node B, an evolved-NodeB (eNB), a next generation Node B (gNB), a sector, a site, a basetransceiver system (BTS), an Access Point (AP), a relay node, a remoteradio head (RRH), a radio unit (RU), a small cell, and the like. In thisspecification, the term “BS” may comprehensively signify some areas orfunctions covered by a Base Station Controller (BSC) in CDMA, a Node-Bin WCDMA, an eNB in LTE, a gNB or sector (site) in NR, and the like, andmay cover all of various coverage areas such as a megacell, a macrocell,a microcell, a picocell, a femtocell and relay node, an RRH, an RU, anda small cell communication range.

The wireless communication device 100 (hereinafter, interchangeably just“device 100” for brevity) may be a UE in the wireless communicationsystem 10. A “UE” may be stationary or mobile, and may refer to variousdevices capable of transmitting and receiving data and/or controlinformation by communicating with the BS. For example, a UE may bereferred to as a terminal equipment, a mobile station (MS), a mobileterminal (MT), a user terminal (UT), a subscriber station (SS), awireless device, a handheld device, and the like.

As shown in FIG. 1A, the wireless communication system 10 may include aplurality of BSs, e.g., 110 and 112, and a system controller 120. Inother examples, the wireless communication system 10 may include one ormore further cells, and a plurality of network entities. The BSs 110 and112 may communicate with device 100 or another cell to transmit andreceive data signals or control information. The wireless communicationdevice 100 may communicate with the wireless communication system 10 andmay also receive signals from a broadcast station 114. Furthermore, thewireless communication device 100 may receive a signal from a satellite130 of a Global Navigation Satellite System (GNSS). Device 100 maysupport radio technologies for various wireless communication.

Technical aspects of the present disclosure may be applied betweencommunication entities forming an uplink channel and a downlink channelin the wireless communication system 10. Hereinafter, device 100 and theBS 110 will be described as communication entities to which technicalaspects of the present disclosure are applied.

A downlink channel 102 and an uplink channel 104 may be formed as a dataconnection path between device 100 and the BS 110. It may be assumedthat the state of the downlink channel 102 and the state of the uplinkchannel 104 are either the same (a reciprocity condition) or similar.When the downlink and uplink channels are similar, this may be referredto as a “calibratable reciprocity condition” in which a calibration maybe performed to effectively achieve reciprocity between the uplink anddownlink channels. Hereafter, whether or not calibration is performed,it may be assumed in the following description that reciprocity exists.(non-reciprocity condition). Reciprocity of the downlink channel 102 andthe uplink channel 104 may exist in a time division duplex (TDD)-basedwireless communication system in which the uplink and the downlink sharethe same frequency spectrum but uplink and downlink transmissions areseparated in the time domain. Reciprocity may also be predicted orachieved via calibration in a frequency division duplex (FDD)-basedwireless communication system in which the uplink and downlink use adifferent frequency spectrum.

The BS 110 may receive a Sounding Reference Signal (SRS) transmittedthrough at least one of a plurality of antennas included in device 100.In embodiments of the present disclosure, the BS 110 typically receivesa sequence of SRSs from at least two of device 100's antennas (a subsetof the antennas), where each antenna transmits one SRS of the sequence.This sequence of SRSs may be referred to as an “SRS switching signal”.For example, when device 100 includes a plurality of antennas, at leasttwo of the antennas may be sequentially selected in a predeterminedorder and each may transmit an SRS, which may be received by the BS 110and in some cases by cells. The BS 110 may estimate the uplink channel104 for each antenna of device 100 and estimate downlink channelinformation using the estimated uplink channel assuming channelreciprocity.

However, even if a transmitter or a receiver is calibrated to satisfychannel reciprocity, channels through which uplink and downlink signalsare transmitted and received may be different due to an implementationproblem of device 100. For example, if the number of transmit/receiveantennas of the terminal is different from the number oftransmit/receive RF chains, or if there is a restriction on the SRSresource allocated from the BS 110, in conventional systems, the BS 110is unable to obtain complete downlink channel information from thesignal received from device 100.

In addition, when the BS 110 limits SRS resources per device to supportmulti-user Multiple Input Multiple Output (MU-MIMO), device 100 isassigned a limited SRS resource, e.g., using less frequencies and/ortime slots for channel measurements as compared to an unrestricted SRSresource situation. When SRS is transmitted in a conventional mannerusing limited resources, beamforming using downlink channel informationobtained by the BS 110 may be suboptimal.

The wireless communication system 10 according to an exemplaryembodiment of the present disclosure efficiently transmits the SRS usingan antenna or beam selection method of device 100 and efficientlyacquires a downlink channel, resulting in beamforming-basedcommunication with improved performance.

Referring further to FIG. 1B, device 100 may include m antennas 1 to m,and the BS 110 may include n antennas 1 to n. Device 100 and the BS 110may perform mutual beamforming-based communication, Multi-Input andMulti-Output (MIMO)-based communication, and the like using respectiveantennas. Because the theoretical channel transmission capacity isincreased through the configuration of FIG. 1B, a transfer rate may beimproved and frequency efficiency may be significantly improved.

The uplink channel h_(j) (1≤j≤m, j is an integer) corresponding to thej-th antenna of the wireless communication device 100 may includechannels h_(1,j), h_(2,j), . . . , h_(n,j) corresponding to therespective n antennas of the BS 110. The BS 110 may receive the SRStransmitted from the j-th antenna of device 100 and estimate the uplinkchannel h_(j) using the received SRS. The BS 110 may estimate a downlinkchannel from the uplink channel h_(j) assuming channel reciprocity,generate a downlink signal using the estimated downlink channel, andtransmit a downlink signal to device 100 through at least one of the nantennas.

Descriptions of the uplink channel h_(j) corresponding to the j-thantenna of device 100 may be applied to uplink channels corresponding toother antennas of device 100, and based on the above, technical conceptsof the present disclosure will be described below.

It is noted, throughout the specification, the terms “antenna selection”and “beam selection” may be used interchangeably. Some technicalconcepts of the present disclosure will be described below mainly withthe use of “antenna selection”.

FIG. 2 is a flowchart illustrating a method of operating device 100 andthe BS 110 in a wireless communication system according to an exemplaryembodiment of the present disclosure. In the method, the wirelesscommunication system 10 may include device 100 and the BS 110, and inoperation S210, device 100 may transmit an “SRS switching signal” to theBS 110 using the SRS switching resource set by the BS 110. (Device 100may have learned of the SRS switching resource during a prior signalexchange with the BS 110.) As noted earlier, an SRS switching signalincludes a plurality of SRSs transmitted in a sequence, where each SRSis transmitted from a respective one of the device 100's antennas. The“SRS switching resource” may be defined as set of uplink resourceelements (REs) (e.g., set of frequencies and/or time slots for SRStransmissions) used when device 100 transmits an SRS signal for thepurpose of obtaining channel information for downlink beamforming by theBS 110. The BS 110 may allocate SRS switching resources to device 100.

According to one embodiment, the available resources of the BS 110 arelimited for the transmission of the SRS switching signal. In thisscenario, there are less SRS switching resources allocated by the BS 110for the SRS switching signal than the number of reception antennas ofdevice 100. In this case, only some antennas are used for transmission(“the first scenario”). For example, supposing there are 5 wirelesscommunication devices in a cell covered by the BS 110 and that 4antennas are included in each wireless communication device 100, ifthere are 16 resources that may be allocated by the BS 110, some of the5 wireless communication devices cannot be allocated 4 SRS switchingresources (assuming switching resources that are to be utilizedsimultaneously).

In another situation, due to a limitation in hardware implementation ofthe wireless communication device 100 when transmitting the SRSswitching signal, there may be a scenario in which only some antennasare used for transmission (“the second scenario”). This corresponds to acase where the number of Tx radio frequency (RF) chains of device 100 isless than the number of reception antennas of 100. For example, due to alimitation in hardware implementation of device 100, the number ofreception antennas is four but the number of transmission antennas maybe limited to two.

In the following discussion, to facilitate understanding of conceptstaught herein, an example is presented in which device 100 has fourreception antennas. In other examples, the concepts are applied to adevice 100 having more or fewer antennas.

Operations of antenna selection and antenna switching will be describedbelow with further reference to FIGS. 3A and 3B.

In operation S220, the BS 110 may estimate uplink channel informationbased on the received SRS switching signal. In operation S230, the BS110 may estimate downlink channel information by performing an operationsuch as calibration from the estimated uplink channel information. Here,calibration refers to a series of processes in which uplink and downlinkchannels are corrected to satisfy reciprocity in an entire signal path,e.g., baseband on transmit to baseband on receive through an RF filter.The BS 110 may determine beamforming using the downlink channelinformation estimated in operation S240, and transmit a channel stateinformation-reference signal (CSI-RS) using beamforming in operation250. Depending on which antenna(s) is selected, the CSI-RS transmittedby the BS 110 to device 100 may include different information.

Device 100 may select a pre-coding matrix indicator (PMI) based on theCSI-RS received in operation S260, and transmit the PMI selected inoperation S270 to the BS 110. When selecting a PMI, device 100 mayconsider information on a selected antenna(s), and accordingly, mayselect an optimal PMI.

In operation S280, the BS 110 may determine the final downlinkbeamforming using information obtained from the SRS switching signalreceived in operation S210 and the information obtained from the PMIreceived in operation S270, and transmit a downlink signal includingdata or the like through an antenna beam determined by the beamformingin operation S290.

The beam determined in operation S280 may be referred to as a “finalbeam” hereinafter, and may be defined in the form of a matrix asfollows.

$\begin{matrix}{x = {F_{SRS}F_{PMI}s}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

F_(SRS) (the number of antennas of the BS 110×the number of CSI-RSantenna ports) may be defined as a matrix for a beam based on the SRSswitching signal received from device 100, and F_(PMI) (the number ofCSI-RS antenna ports×the number of data layers or data streams) may bedefined as a matrix for a beam based on a PMI received from device 100.s (the number of data layers or data streams×1) may be defined as amatrix for a downlink signal including data that the BS 110 is totransmit to device 100.

The BS 110 may form a finally synthesized beam using all of theinformation obtained from the SRS switching signal and the PMI, and mayperform beamforming with device 100. F_(SRS) and F_(PMI) may beexpressed as F_(SRS_PMI), which is a matrix for the finally synthesizedbeam, that is, in the form of one beam. x (the number of BS antennas×1)corresponds to the final signal transmitted from the BS 110 to device100.

According to the above operation method, device 100 adaptively transmitsthe SRS switching signal and adaptively transmits the PMI to optimizethe acquisition of downlink channel information and the beamformingdecision of the BS 110.

Meanwhile, the CSI-RS corresponding to the downlink reference signal andthe SRS corresponding to the uplink reference signal described withreference to FIG. 2 are only examples of reference signals that may beapplied in the method. Alternative reference signals may include a pilotsignal transmitted by a BS in a downlink for channel estimation and apilot signal transmitted in an uplink by a wireless communication devicefor channel estimation.

FIGS. 3A and 3B are flowcharts illustrating examples of a method oftransmitting an SRS switching signal according to exemplary embodimentsof the present disclosure.

FIG. 3A illustrates a process of determining an antenna subset to selectan antenna for transmitting an SRS switching signal in operation S210 ofFIG. 2.

In operation S310 a, a BS 110 a may transmit a downlink reference signalto a wireless communication device 100 a (hereafter, “device 100 a”).Device 100 a may estimate the downlink channel information from thereceived CSI-RS in operation S320 a, and determine the antenna subsetbased on the estimated downlink channel information in operation S330 a.The antenna subset may be determined based on at least one of a signalto interference plus noise ratio (SINR) of the wireless communicationdevice, a transmission/reception characteristic of an antenna, and alinearity of a transmission power amplifier. In operation S340 a, device100 a may transmit the SRS switching signal through at least one ofantennas included in the determined antenna subset.

In an exemplary embodiment, a method of determining an antenna subsetmay include a method of sequentially determining the antenna subset andthen switching the antenna subset according to the transmission periodof the SRS switching signal, a method of aperiodic switching of theantenna subset after determining an antenna subset based on a gain valueof/signal quality metric for a specific beam, a method of switching anantenna subset after determining an antenna subset according to spatialcorrelation between reception antennas of a wireless communicationdevice, and a method of switching antenna subsets according to an updateperiod after determining an antenna subset based on reinforcementlearning. Detailed descriptions of this are provided below withreference to FIG. 4.

Referring to FIG. 3B, a process of selecting a beam to transmit an SRSswitching signal in operation S210 of FIG. 2 is illustrated.

In operation S310 b, a BS 110 b may transmit a downlink reference signalto a wireless communication device 100 b (“device 100 b”). Device 100 bmay estimate the downlink channel information from the received CSI-RSin operation S320 b, and determine a beam for transmitting the SRSswitching signal from each antenna based on the estimated downlinkchannel information in operation S330 b. For instance, 100 b selects abeam with good reception performance and spatial characteristics from apreviously designed beam code-book using the estimated downlink channelinformation, or may be newly designed when there is no pre-designed beamcodebook. In operation S340 b, the SRS switching signal may betransmitted using the determined beam.

Table 1 below shows a beam codebook according to an embodiment of thepresent disclosure.

TABLE 1 Beam#1 Beam#2 Beam#3 Beam#4 Antenna#1 A11 + B11i A12 + B12iA13 + B13i A14 + B14i  Antenna#2 A21 + B21i A22 + B22i A23 + B23i A24 +B24i  Antenna#3 A31 + B31i A32 + B32i A33 + B33i A34 + B34i  Antenna#4A41 + B41i A42 + B42i B43 + B43i A44 + B44ii

Referring to Table 1, in this example it is assumed there are fourantennas of device 100 b and four beams that may be formed from eachantenna. For example, the beam codebook includes an index of a precodingmatrix shared in advance in device 100 b and the BS 110 b. Elements ofeach antenna for beam configuration may be expressed as arbitrarycomplex values. For example, the real component for the second beam ofAntenna #4 is A42 and the imaginary component is B42.

Table 2 below shows a beam codebook according to an embodiment of thepresent disclosure.

TABLE 2 Beam#1 Beam#2 Beam#3 Beam#4 Antenna#1 1 1 1 1 Antenna#2 1 −1i −1  1i Antenna#3 1 −1 1 −1 Antenna#4 1   1i −1 −1i

Referring to Table 2, among the elements of the third antenna forconfiguring the beam, an element for the third beam may be composed of1.

FIG. 4 is a flowchart illustrating an example of a method oftransmitting an SRS switching signal according to a sequential antennaselection method according to an exemplary embodiment of the presentdisclosure.

The example of FIG. 4 shows a method of transmitting an SRS switchingsignal according to a method of sequentially determining an antennasubset and then switching the antenna subset according to an SRStransmission period. This may be referred to as a “sequential antennaselection method”.

In FIG. 4, it is assumed that the number of reception antennas of device100 is 4, and an SRS switching signal is transmitted to the BS 110 byusing two transmission antennas that are less than the number ofreception antennas. That is, it is assumed that the size of the antennasubset determined by device 100 is 2. For example, this correspond to acase where only two antennas are used when the BS 110 allocates two SRSswitching resources to device 100 (first scenario), or due to a hardwareimplementation limitation of device 100.

In an embodiment, when the indices of the first antenna, the secondantenna, the third antenna, and the fourth antenna are {0, 1, 2, 3},respectively, a subset consisting of a combination of two antennas fortransmitting an SRS switching signal among the first to fourth antennasmay be configured as follows.

Antenna subset: {0, 1} {0, 2} {0, 3} {1, 2} {1, 3} {2, 3}

In an exemplary embodiment, device 100 may sequentially determine eachof the six possible antenna subsets in a predefined order.

Here, the fact that the antenna subset is sequentially determined, forexample, means that the six possible antenna subsets are sequentiallyselected for each transmission period of the SRS switching signal among{0, 1} {0, 2} {0, 3} {1, 2} {1, 3}, and {2, 3}.

For example, in operation S402, 100 may determine an antenna subset totransmit the SRS switching signal as {0, 1} in the first SRS switchingtransmission period. That is, device 100 may determine to transmit theSRS switching signal by using the first antenna and the second antennaamong the four antennas. In some embodiments, device 100 may determineeach of the antenna subsets in a different order than that describedabove.

In operation S404, after transmitting SRS_0, which is an SRS switchingsignal using the first antenna, and SRS_1, which is an SRS switchingsignal using a second antenna, the BS 110 may design a downlink beamF_SRS using SRS_0 and SRS_1 in operation S406. The BS 110 may transmitthe CSI-RS through the F_SRS beam in operation S408.

Device 100 may select a PMI based on the CSI-RS received in operationS410, and feed back the PMI to the BS 110 in operation S412. The BS 110may design the downlink beam F_PMI using the PMI received in operationS414, and transmit a downlink signal including data to device 100 byusing the final beam determined by F_SRS and F_PMI in operation S416.

As an exemplary embodiment, operations S402 to S416 may be performed bydevice 100 for a time corresponding to the first SRS switching signaltransmission period, and may be referred to as Cycle 1. In the secondSRS switching signal transmission period corresponding to Cycle 2, theantenna subset {0, 2} is determined to transmit the SRS switchingsignal, and for example, in Cycle 4 corresponding to the fourth SRSswitching signal transmission period, the antenna subset {1, 2} isdetermined to transmit SRS_1 and SRS_2 to the BS 110.

In operation S418, device 100 may determine an antenna subset totransmit the SRS switching signal as {1, 2} in the fourth SRS switchingtransmission period after several SRS switching transmission periods arerepeated. That is, device 100 may determine to transmit the SRSswitching signal by using the second antenna and the third antenna amongthe four antennas. In some embodiments, device 100 may determine each ofthe antenna subsets in a different order than that described above.

In operation S420, after transmitting SRS_0, which is an SRS switchingsignal using the first antenna, and SRS_1, which is an SRS switchingsignal using a second antenna, the BS 110 may design a downlink beamF_SRS using SRS_0 and SRS_1 in operation S422. The BS 110 may transmitthe CSI-RS through the F_SRS beam in operation S424.

Device 100 may select a PMI based on the CSI-RS received in operationS426, and feed back the PMI to the BS 110 in operation S428. The BS 110may design the downlink beam F_PMI using the PMI received in operationS430, and transmit a downlink signal including data to the wirelesscommunication device 100 by using the final beam determined by F_SRS andF_PMI in operation S432.

According to the method shown in FIG. 4, device 100 may monitor the“gain” of the final beam at every SRS switching signal transmissionperiod and sequentially consider all possible antenna subsets to find anoptimal antenna combination. Here, “beam gain” or just “gain” or “gainvalue” may be defined as a relative term (since the distance between theBS 110 and device 100 is typically unknown) for signal quality of thesignal transmitted by an antenna beam transmitted from a base stationand received by a wireless communication device (e.g., 100). Hereafter,the terms “gain” and “signal quality” may be used interchangeably. Gainmay be determined by the power of a signal received by device 100, asignal to noise ratio (SNR) of the signal received by device 100, asignal to noise and interference ratio (SINR) or the signal received bydevice 100, and/or frequency efficiency.

According to embodiments of the present disclosure, an antenna subsetfinally selected as an optimal antenna combination may be referred to asa “final antenna subset”.

Note that in the above example, an antenna subset size of 2 was used toaid in understanding concepts taught herein. In other examples, more orfewer antennas may form an antenna subset.

FIGS. 5A and 5B are flowcharts illustrating examples of a method oftransmitting an SRS switching signal according to an opportunisticantenna selection method according to exemplary embodiments of thepresent disclosure.

FIG. 5A illustrates a method of transmitting an SRS switching signalaccording to a method of aperiodic switching of the antenna subset afterdetermining an antenna subset based on a gain value of a specific beam.This may be referred to as one of the “opportunistic antenna selectionmethods”.

In the opportunistic antenna selection method, a specific valuecorresponding to the gain value of the beam is preset as a thresholdvalue B_(th), and when it is determined that the gain value of the finalbeam determined as an arbitrary antenna subset is less than thethreshold value, regardless of the order, it may immediately decide to adifferent antenna subset. When it is determined that the gain value ofthe final beam determined as an arbitrary antenna subset is greater thanthe threshold value, the process for determining another antenna subsetand transmitting the SRS switching signal may be stopped, and acorresponding antenna subset may be declared as an optimal antennacombination. That is, the corresponding antenna subset may be determinedas the “final antenna subset”.

Meanwhile, after the final antenna subset is determined, device 100 maytrack an optimal antenna combination with an arbitrary tracking period.There may be a method of changing one antenna included in the previouslydetermined final antenna subset, and there may be a method of changingone or more antennas. When the gain of the final beam is rapidlylowered, an antenna included in the previously determined final antennasubset may not be selected, or the final antenna subset itself may bereplaced with another antenna subset. Tracking and a tracking period maybe determined from an indicator related to a change in a radio channel.

Specifically, referring to FIG. 5A, device 100 may determine anarbitrary antenna subset for transmitting the SRS switching signal inoperation S510 a, and after operation S510 a, operations S210 to S290described with reference to FIG. 2 may be performed, and detailedinformation thereof will be omitted.

In operation S520 a, device 100 may monitor the gain value of the finalbeam received in operation S290, as an exemplary embodiment. Inoperation S530 a, device 100 may determine whether the gain value of themonitored final beam exceeds the threshold value B_(th).

In operation S540 a, when the gain value of the final beam monitored bydevice 100 exceeds the threshold value B_(th), the antenna subsetdetermined in operation S510 a may be determined as the final antennasubset.

On the other hand, when the gain value of the final beam monitored bydevice 100 is less than or equal to the threshold value B_(th), theprocess returns to operation S510 a of determining an antenna subset.For example, device 100 may return to operation S510 a, select anantenna subset {2, 3}, and transmit the SRS switching signal using thethird antenna and the fourth antenna.

FIG. 5B illustrates a method of transmitting an SRS switching signalaccording to a method of aperiodic switching of the antenna subset afterdetermining an antenna subset based on the values of channel gainscorresponding to all antennas for a channel receiving CSI-RS. This maybe referred to as one of the “opportunistic antenna selection methods”.

In an embodiment, when channel gains corresponding to all antennas for achannel receiving a CSI-RS have similar values, device 100 may determinethe antenna subset determined in an operation akin to S510 b as thefinal antenna subset. The criterion for whether channel gains havesimilar values may be set differently according to embodiments.

On the other hand, when the channel gains corresponding to all antennasfor the channel receiving the CSI-RS have a relatively large difference,device 100 may return to an operation akin to S510 b of determining theantenna subset and continuously attempt to transmit the SRS switchingsignal using the new antenna subset.

Device 100 may determine an arbitrary antenna subset for transmittingthe SRS switching signal in operation S510 b, and after operation S510b, operations S210 to S290 described with reference to FIG. 2 may beperformed (detailed descriptions thereof are omitted here).

In operation S520 b, device 100 may monitor a gain value of a channelthat receives a CSI-RS in operation S290, as an exemplary embodiment. Inoperation S530 b, device 100 may determine whether the absolute value ofthe difference between the monitored channel gain values exceeds thethreshold value C_(th).

When the absolute value of the difference between the gain values of thechannel monitored in operation S520 b exceeds the threshold valueC_(th), in operation S540 b, device 100 may determine the final antennasubset as the antenna subset determined in operation S510 b.

On the other hand, when the gain value of the final beam monitored bydevice 100 is less than or equal to the threshold value B_(th), theprocess returns to operation S510 b of determining an antenna subset.For example, device 100 may return to operation S510 b, select anantenna subset {2, 3}, and thereafter, periodically or continuouslytransmit the SRS switching signal using the third antenna and the fourthantenna.

Meanwhile, after the final antenna subset is determined, device 100 maytrack an optimal antenna combination with an arbitrary tracking period.This may employ a method of changing one antenna included in thepreviously determined final antenna subset, or a method of changing oneor more antennas. During tracking, when the gain of the final beam israpidly lowered, an antenna included in the previously determined finalantenna subset may not be selected, or the final antenna subset itselfmay be replaced with another antenna subset. Tracking and a trackingperiod may be determined from an indicator related to a change in aradio channel.

FIG. 6 is a flowchart illustrating an example of a method oftransmitting an SRS switching signal according to an antenna spatialcorrelation-based selection method according to an exemplary embodimentof the present disclosure.

Specifically, FIG. 6 illustrates a method of transmitting an SRSswitching signal according to a method of switching an antenna subset(“Method 3”) after determining an antenna subset according to spatialcorrelation between reception antennas of a wireless communicationdevice. Method 3 may be referred to as “an antenna spatialcorrelation-based selection method”.

Spatial correlation between antennas may be defined as an indexindicating the degree of interference between antennas determined byfactors such as a distance between antennas. For example, when thespatial correlation between antennas is low, different signals may beindependently transmitted through the antennas. Accordingly, low spatialcorrelation between antennas is desirable for an antenna subset of anSRS switching signal according to embodiments of the present disclosure.A method of considering spatial correlation between antennas may have anobjective of transmitting a signal through an antenna that guarantees arelatively independent channel by selecting a combination of antennasaccording to channel information.

Spatial correlation between antennas may be determined by a frequencyband, a cell type covered by the BS, a separation distance betweenantennas, polarization, and the like.

According to an embodiment, antenna subsets may be arranged in an orderof lowest to highest spatial correlation between reception antennas ofdevice 100 and then sequentially determined as an antenna subset totransmit the SRS switching signal.

Alternatively, antenna subsets may be arranged in an order of highest tolowest spatial correlation between reception antennas of device 100 andthen sequentially determined as an antenna subset to transmit the SRSswitching signal.

In another embodiment, the antenna subset may be switched consideringthe arrangement of a plurality of antennas of device 100 withoutmeasuring spatial correlation. For example, antenna subsets may bearranged from the antenna combinations having the largest antennaseparation distance values in the following order.

Antenna subset: {0, 3} {0, 2} {1, 3} {0, 1} {1, 2} {2, 3}

Referring to FIG. 6, in operation S610, device 100 may arrange antennasubsets in an order of low correlation between antennas. In operationS620, one of the antenna subsets listed in operation S610 issequentially selected and determined as the i-th antenna subset. Afteroperation S620, operations S210 to S290 described with reference to FIG.2 may be performed (redundant descriptions thereof are omitted).

In operation S630, device 100 monitors the gain value of the final beam.For example, assuming that the number of antennas included in device 100is 4 and the antenna subset is a combination of two antennas, there area total of six possible antenna subsets, and operations S620 to S630 arerepeated a total of six times.

When monitoring of the final beam gain value for all antenna subsets iscomplete, in operation S640, the antenna subset having the largest gainvalue may be determined as the final antenna subset.

Meanwhile, after the final antenna subset is determined, device 100 maytrack an optimal antenna combination with an arbitrary tracking period.This may employ a method of changing one antenna included in thepreviously determined final antenna subset, or a method of changing oneor more antennas. During tracking, when the gain of the final beam israpidly lowered, an antenna included in the previously determined finalantenna subset may not be selected, or the final antenna subset itselfmay be replaced with another antenna subset. Tracking and a trackingperiod may be determined from an indicator related to a change in aradio channel.

Also, according to one embodiment, if there is one SRS switchingresource allocated by the BS 110 for the SRS switching signal accordingto the “first scenario” (mentioned earlier), after determining theantenna subset based on the reception performance of the antenna, device100 may switch the antenna subset to transmit the SRS switching signal.For example, antenna subsets may be sequentially determined afterantennas having high antenna reception power are arranged in ascendingorder or antennas having small antenna reception power are arranged inascending order.

FIGS. 7A to 7C are flowcharts illustrating examples of a method oftransmitting an SRS switching signal according to an antenna selectionmethod based on reinforcement learning according to exemplaryembodiments of the present disclosure.

Referring to FIGS. 7A to 7C, after determining the antenna subset basedon reinforcement learning according to the method of switching theantenna subset according to the update period, the SRS switching signalmay be transmitted, which may be referred to as a “reinforcementlearning-based antenna selection method”.

Reinforcement learning is a type of machine learning, and may be definedas a method in which an agent defined in a certain environmentrecognizes the current state and selects an action or action sequencethat maximizes Reward among the selectable actions. The reinforcementlearning may be performed by the reinforcement learning device 810 c ofdevice 100, and the operation of the reinforcement learning device 810 cwill be described later with reference to FIG. 8C.

The antenna selection method based on reinforcement learning includes aQ-learning-based antenna selection method and a Bandit learning-basedantenna selection method according to an embodiment of the presentdisclosure.

FIG. 7A is a flowchart illustrating a method of transmitting an SRSswitching signal according to a Q-learning-based antenna selectionmethod during reinforcement learning.

The Q function expressed as “(state, action)”, which is a pair of Stateand Action, may be defined as a function that may predict the expectedvalue of the utility that executing a given action in a given state willprovide. According to an embodiment, device 100 may select an antennacombination having a large Q value, that is, Q(S, A).

In an embodiment, the Action may be defined as an action of selecting anantenna combination for determining an antenna subset, and State, whichmeans a state when a specific antenna is selected, may be defined as aparameter related to a downlink channel. The parameters related to thedownlink channel may be determined by correlation in the time, space,and frequency domain, and the strength of the downlink signal. Rewardmay be defined as a reception performance index for a CSI-RS receivedfrom device 100 or a downlink signal including data received using afinal beam. The reception performance for the downlink signal may bedetermined by a block error rate (BLER), frequency efficiency, andstrength of the downlink signal.

Table 2 shows a Q-table according to an embodiment of the presentdisclosure.

TABLE 2 A_1 A_2 . . . A_N S_1 Q(S_1, A_1) Q(S_1, A_2) . . . Q(S_1, A_N). . . . . . . . . . . . . . . S_M Q(S_M, A_1) Q(S_M, A_2) . . . Q(S_M,A_N)

Referring to Table 2, for example, A_1 may mean a case where the antennasubset determined by device 100 is {0,1}. S_1 may mean a statecorresponding to one of downlink-related parameter values that exist asmany as M of possible cases due to various factors such as correlationin the time, space, frequency domain, and strength of a downlink signal.

Q(S_M, A_N) takes an action of selecting an antenna subset that includesthe Nth antenna combination, and may mean a Q value in the case of astate corresponding to a parameter numbered by M based on the antennacombination.

In an exemplary embodiment, the update operation of Q may be expressedas follows.

$\begin{matrix}\left. {Q_{new}\left( {S,A} \right)}\leftarrow{{Q_{old}\left( {S,A} \right)} + {\alpha\left\lbrack {R + {\gamma\;{\max\limits_{A}{Q\left( {S^{\prime},A} \right)}}} - {Q_{old}\left( {S,A} \right)}} \right\rbrack}} \right. & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

α may be defined as a learning rate factor, and may have a value greaterthan 0 and less than or equal to 1. R corresponds to a Reward value, andγ is a discount factor, and may be defined as a value indicating howimportant a present reward is than a reward obtained in the future.Q(S′,A) may be defined as the optimal Q value expected in the futurestate S′.

Specifically, device 100 may initialize Q (S,A) to an arbitrary value inoperation S710 a, which is the first operation of the Q-learning-basedalgorithm. After initializing Q, the following processes for eachepisode are repeated:

In operation S720 a, device 100 selects whether to take an actionrandomly with a probability of e or whether to take an action thatsatisfies

$\begin{matrix}{A = {\arg_{A}^{\max}{Q\left( {S,A} \right)}}} & \;\end{matrix}$

with a probability of (1−e). In operation S730 a, device 100 observesReward according to the selected Action and the new state value S′, andupdates the Q value using [Equation 2] in operation S740 a, that is,calculate Q_(new)(S,A). Device 100 determines whether the episode hasended in operation 750 a, and if device 100 determines that the episodehas not ended, S′ is updated to S in operation S760 a.

According to an embodiment, device 100 may select an antenna combinationconstituting an antenna subset based on Q, and after the antenna subsetis determined, calculate State and Reward and updates Q to determineanother antenna subset based on the updated Q.

FIG. 7B is a flowchart illustrating a method of transmitting an SRSswitching signal according to an antenna selection method based on anUpper Confidence Bound (UCB) algorithm during reinforcement learning.

The UCB algorithm may be defined as an algorithm that finds an upperlimit value with a high probability of an expected reward at a specifictime t, that is, an UCB value, from observation results during thattime. For example, the UCB is updated for each action that selects anantenna combination included in the antenna subset, and device 100 mayselect an antenna subset including an antenna combination having a largeUCB. This may be referred to as one of “Bandit learning-based antennaselection methods”.

In an exemplary embodiment, the UCB value may be expressed as follows.

$\begin{matrix}{{UB{C_{k}(t)}} = \left\{ \begin{matrix}{\infty,} & {{{if}\mspace{14mu}{T_{k}\left( {t - 1} \right)}} > 0} \\{{{\hat{\mu_{k}}\left( {t - 1} \right)} + \sqrt{\frac{2\ln\;\left( \frac{1}{\delta} \right)}{T_{k}\left( {t - 1} \right)}}},} & {{{if}\mspace{14mu}{T_{k}\left( {t - 1} \right)}} > 0}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In an exemplary embodiment, Reward and an empirical mean of Reward maybe expressed as follows.

$\begin{matrix}{{{{\overset{\hat{}}{\mu}}_{k}\left( {t + 1} \right)} = {\frac{1}{T_{k}\left( {t + 1} \right)}{\sum\limits_{t = 1}^{T_{k}{({t + 1})}}{X_{k}(t)}}}},{{{where}\mspace{14mu}{T_{k}\left( {t + 1} \right)}} = {{T_{k}(t)} + 1}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

T_(k)(t) may be defined as the number of times a corresponding antennasubset is selected up to time t, and S may be defined as a learningparameter. In addition, X_(k)(t) may be defined as the observed Rewardfor the k-th Action at time t. In addition, {circumflex over (μ)}_(k)(t)may be defined as an empirical mean of Reward accumulated up to time t.

For example, device 100 may calculate the UCB at time tin operation S710b, and may select a combination of antennas that maximizes thecalculated UCB in operation S720 b. In addition, device 100 may measurea CSI-RS channel by selecting one of the antenna combinations selectedin operation S730 b. Device 100 may calculate Reward and an empiricalmean of Reward using [Equation 4] in operation S740 b.

The UCB algorithm may operate in operations S710 b to S740 b, andoperations S710 b to S740 b may be repeated for an arbitrary number oftimes.

FIG. 7C is a flowchart illustrating a method of transmitting an SRSswitching signal according to a probability distribution-based antennaselection method during reinforcement learning.

As an embodiment, device 100 may determine an antenna subset by using avalue representing a preference for selection of an antenna combinationas a probability. This may be referred to as one of “Banditlearning-based antenna selection methods”.

The initial probability for the preference may be arbitrarily set as

${{p_{k}(t)} = \frac{1}{K}},$

where K may be defined as the number of antenna combinations, that is,the number of all possible antenna subsets. In operation S710 c, device100 may determine an antenna subset including an antenna combinationselected according to the learned probability distribution.

As an exemplary embodiment, the probability for preference may beexpressed as follows.

$\begin{matrix}{{p_{k}(t)} = {{\left( {1 - \gamma} \right)\frac{\exp\left( {\rho\;{{\hat{S}}_{k}(t)}} \right)}{\sum\limits_{j = 1}^{K}{\exp\left( {{\hat{S}}_{j}(t)} \right)}}} + \frac{\gamma}{K}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In operation S720 c, device 100 may set a Positive Reward or NegativeReward {circumflex over (X)}_(k)(t) according to an index indicating theperformance of the CSI-RS channel allocated the selected antennacombination. For example, an index indicating the performance of theCSI-RS channel may include a signal to interference plus noise ratio(SINR).

In an exemplary embodiment, Reward may be calculated as follows.

$\begin{matrix}{{{\hat{X}}_{k}(t)} = \left\{ \begin{matrix}{\frac{\alpha}{p_{k}(t)},\ {{{if}\mspace{14mu}{SIN}\; R_{k}} \geq \tau}} \\{\frac{- \beta}{1 - {p_{k}(t)}},\ {{{if}\mspace{14mu}{SIN}\; R_{k}} < \tau}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In operation S720 c, device 100 may calculate Reward according to theperformance of the CSI-RS channel using [Equation 6].

In addition, optionally, device 100 may update Reward of the antennacombination having a high relevance in operation S730 c by introducing aweight w. For example, Reward may be updated by multiplying the (k−1)-thReward and the (k+1)-th Reward by weights w₁ and w₂, respectively. Next,device 100 updates the probability distribution value by accumulatingRewards for a predetermined time in operation S740 c.

As an exemplary embodiment, the probability distribution of accumulatedRewards may be expressed as follows.

$\begin{matrix}{{{{\hat{S}}_{k}(t)} = {\sum\limits_{t = 1}^{T}{{\hat{X}}_{k}(t)}}},\ {k = 1},\ldots\mspace{14mu},\ K} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

The probability distribution-based antenna selection method may operatein operations S710 c to S740 c, and operations S710 c to S740 c may berepeated for an arbitrary number of times.

In the above-described plurality of reinforcement learning-based antennaselection schemes, Action may be applied by extending to an action ofselecting an antenna combination for determining an antenna subset andselecting transmission power. For example, Action may be defined asfollows.

Action_i: Selecting the first and third antennas & selecting thetransmission power of the first antenna as P_level4 and selecting thetransmission power of the third antenna as P_level2

Action_j: Selecting the 0-th antenna and the third antenna & Selectingthe transmission power of the 0-th antenna as P_level1 and thetransmission power of the third antenna as P_level2

For example, P_level2 may mean power corresponding to level2 set bydevice 100.

FIG. 8 is a flowchart illustrating an example of a method of tracking afinal antenna subset according to an exemplary embodiment of the presentdisclosure.

Referring to FIG. 8, a method of tracking a final antenna subsetdetermined through the methods described with reference to FIGS. 4 to 7Cis shown.

Through the embodiments of FIGS. 4 to 7C, in operation S810, device 100may determine a final antenna subset configured with an optimal antennacombination. After the final antenna subset is determined, in operationS820, device 100 may track the optimal antenna combination with anarbitrary tracking period, and in operation S830, one antenna includedin the final antenna subset previously determined or one or moreantennas may be changed according to the tracking result.

As an embodiment, when the gain of the final beam is rapidly lowered, anantenna included in the previously determined final antenna subset maynot be selected, or the final antenna subset itself may be replaced withanother antenna subset. For example, if the antenna subset size is 3,the antenna may be changed to one, changed to two, or changed to adifferent antenna subset with a different antenna subset size of 3.Tracking and a period are determined from an indicator related to achange in a radio channel, and the tracking period may be a valuecorresponding to several times the transmission period of the SRSswitching signal. For example, the tracking period may be determinedaccording to the Doppler characteristic, which is an index according tothe time change of the radio channel, and when the Doppler transitionvalue of the wireless communication device is large, the tracking periodmay be set short, and when the Doppler transition value is small, thetracking period may be set longer.

FIGS. 9A and 9B are flowcharts illustrating examples of a method ofselecting a pre-coding matrix indicator (PMI) according to exemplaryembodiments of the present disclosure.

When 100 a and 100 b transmit the SRS using limited SRS resources andantennas due to the limitations of the scenarios 1 and 2 describedabove, beamforming using the downlink channel information obtained bythe BS causes loss. Accordingly, the method of selecting a PMI forminimizing signal loss using downlink beamforming received by devices100 a and 100 b may include a PMI selection method applying weightsaccording to channels, a PMI selection method based on reinforcementlearning, and the like.

FIG. 9A is a flowchart showing a method of selecting a PMI to which aweight is applied according to an exemplary embodiment of the presentdisclosure.

Referring to FIG. 9A, an example of a PMI selection method forminimizing redundancy of information received by device 100 a andminimizing signal loss using beamforming is illustrated. Specifically, aPMI may be selected by applying different weights to channelscorresponding to an antenna used for transmission of the SRS switchingsignal and an antenna not used for transmission of the SRS switchingsignal.

For example, in operation S902 a, device 100 a may determine an antennasubset to transmit the SRS switching signal as {0, 1} in the first SRSswitching transmission period. In operation S904 a, after transmittingSRS_0, which is an SRS switching signal using the first antenna, andSRS_1, which is an SRS switching signal using a second antenna, the BS110 may design a downlink beam F_SRS using SRS_0 and SRS_1 in operationS906 a. The BS 110 a may transmit the CSI-RS through the F_SRS beam inoperation S908 a. Assuming that the channels used for CSI-RS receptionare h0, h1, h2, and h3, in operation S910 a, device 100 a may setweights applied to each channel to w0, w1, w2, and w3. w0 to w3 may bedetermined according to selection and use when transmitting the SRSswitching signal. For example, the weights w0 and w1 of the first andsecond antennas used for transmitting the SRS switching signal, and theweights w2 and w3 of the third and fourth antennas not used fortransmitting the SRS switching signal may be set differently. Inoperation S912 a, device 100 a may select the PMI using informationobtained by applying a weight to each channel [w0×h0, w1×h1, w2×h2,w3×h3], and feed back the selected PMI to the BS 110 a in operation S914a.

According to an embodiment, the weight may be set to have a larger valueas the gain of the channel corresponding to the antenna is smaller.Alternatively, the weights may be set so that the gains of channelscorresponding to the weighted antennas are all the same.

FIG. 9B is a flowchart showing a method of selecting a PMI based onreinforcement learning according to an exemplary embodiment of thepresent disclosure.

Referring to FIG. 9B, as in the antenna combination selection method, amethod of selecting a PMI based on reinforcement learning isillustrated.

According to an embodiment, in operation S902 b, device 100 b maydetermine an antenna subset to transmit the SRS switching signal as {0,1} in the first SRS switching transmission period. In operation S904 b,after transmitting SRS_0, which is an SRS switching signal using thefirst antenna, and SRS_1, which is an SRS switching signal using asecond antenna, the BS 110 b may design a downlink beam F_SRS usingSRS_0 and SRS_1 in operation S906 b. The BS 110 b may transmit theCSI-RS through the F_SRS beam in operation S908 b. In operation S912 a,device 100 may select a PMI using reinforcement learning. Specifically,UCB-based among Q-learning and bandit learning, and gradient banditlearning-based among bandit learning PMI selection methods may all beapplied. As an example, Action may be defined as an action that selectsPMI, and State may be defined as a performance index for a channel inwhich a CSI-RS signal is received, and Reward may be defined as aperformance index for a channel in which a downlink signal is receivedusing a final beam. That is, device 100 b may select a PMI thatmaximizes the “performance of the final beam reception channel”corresponding to Reward among selectable PMIs by recognizing Staterepresenting the performance of the channel used for receiving theCSI-RS signal. The wireless communication device 100 b may feed back theselected PMI to the BS 110 b in operation S914 a.

FIGS. 10A to 10C are block diagrams illustrating structures of awireless communication device according to exemplary embodiments of thepresent disclosure.

FIG. 10A is a block diagram showing structures of a wirelesscommunication device based on an antenna selection method according toan exemplary embodiment of the present disclosure.

Referring to FIG. 10A, device 100 a may include first to m-th antennas 1to m, a radio-frequency integrated circuit (RFIC) 1002 a, and aprocessor 1006 a. The RFIC 1002 a may include a switching network 1004 aand first to n-th RF chains. The RFIC 1002 a may include a plurality ofRF chains, and device 100 a may include a plurality of RFICs. Theswitching network 1004 a may be connected to the first to m-th antennas1 to m. In some cases, only one RF chain may be in the RFIC 1002 a, ormay be connected to each individual antenna.

The processor 1006 a according to the exemplary embodiment of thepresent disclosure may identify the downlink reference signal from theSRS switching resource set by the BS 110 a. The processor 1006 a maygenerate downlink channel information using the downlink referencesignal, select an antenna combination including at least one of thefirst to m-th antennas 1 to m, determine an antenna subset including thecorresponding antenna combination, and control the switching network1004 a based on the determined antenna subset.

The switching network 1004 a according to an exemplary embodiment of thepresent disclosure may be connected to the processor 1006 a. Also, theswitching network 1004 a may select at least one of the antennasincluded in the antenna subset determined by the processor 1006 a. TheSRS switching signal may be transmitted to the BS 110 a through theselected antenna.

The processor 1006 a according to an embodiment of the presentdisclosure may select a PMI based on the CSI-RS received from the BS 110a using the first beam, and may transmit the selected PMI to the BS. TheBS 110 a may transmit a downlink signal including data or the like usingthe final beam, and the processor 1006 a may process the receiveddownlink signal. The final beam may be determined by informationobtained from the SRS switching signal and information obtained from thePMI.

FIG. 10B is a block diagram showing structures of a wirelesscommunication device based on a beam selection method according to anexemplary embodiment of the present disclosure.

Referring to FIG. 10B, device 100 b may include first to m-th antennas 1to m, an RFIC 1002 b, and a processor 1006 b. The RFIC 1002 b mayinclude a beamformer 1004 b and first to n-th RF chains. The RFIC 1002 bmay include a plurality of RF chains, and device 100 b may include aplurality of RFICs. The beamformer 1004 b may be connected to the firstto m-th antennas 1 to m. In some cases, only one RF chain may be in theRFIC 1002 b, or may be connected to each individual antenna.

The processor 1006 b according to the exemplary embodiment of thepresent disclosure may identify the downlink reference signal from theSRS switching resource set by the BS 110 b. The processor 1006 b maygenerate downlink channel information using the downlink referencesignal, and may select a beam using the previously shared beam codebookinformation. The processor 1006 b may design an optimal beam when thereis no pre-shared beam code book. The processor 1006 b may design a newbeam considering reception performance and spatial characteristics, andmay control the beamformer 1004 b based on the determined beam.

The beamformer 1004 b according to an exemplary embodiment of thepresent disclosure may be connected to the processor 1006 b. Inaddition, the beamformer 1004 b may form a beam according to beaminformation selected (or designed) by the processor 1006 b. The SRSswitching signal may be transmitted to the BS 110 b through the formedbeam.

The processor 1006 b according to an embodiment of the presentdisclosure may select a PMI based on the CSI-RS received from the BS 110b using the first beam, and may transmit the selected PMI to the BS. TheBS 110 b may transmit a downlink signal including data or the like usingthe final beam, and the processor 1006 b may process the receiveddownlink signal. The final beam may be determined by informationobtained from the SRS switching signal and information obtained from thePMI.

FIG. 10C is a block diagram showing structures of a wirelesscommunication device based on a reinforcement learning method accordingto an exemplary embodiment of the present disclosure.

Referring to FIG. 10C, a wireless communication device 100 c may includefirst to m-th antennas 1 to m, an RFIC 1002 c, and a processor 1006 c.The processor 1006 c may include a machine learning device 1010 c forperforming the reinforcement learning-based antenna selection method,the reinforcement learning-based beam selection method, or thereinforcement learning-based PMI selection method.

For example, the machine learning device 1010 c may observe State,select an Action, and calculate Reward and Q in order to perform theQ-learning-based antenna selection method of FIG. 7A. That is, themachine learning device 910 c may perform the operations forreinforcement learning disclosed in FIGS. 7A to 7C and 8B, and detaileddescriptions thereof will be omitted.

As an example, in the Q-learning-based antenna selection method of FIG.7A, the machine learning device 910 c may calculate Q(S,A) having thelargest value in a given state using the Q-table in [Table 2], andselect an antenna combination corresponding to the corresponding Q valuebased on the learned information.

While the inventive concept has been particularly shown and describedwith reference to embodiments thereof, it will be understood thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims and theirequivalents.

1. A method of operating a wireless communication device including aplurality of antennas, the method comprising: determining an antennasubset including at least one of the plurality of antennas; transmittinga sounding reference signal (SRS) switching signal to a base stationthrough at least one antenna of the antenna subset; receiving a channelstate information-reference signal (CSI-RS) transmitted from the basestation through a first beam; selecting a precoding matrix indicator(PMI) based on the CSI-RS; transmitting the selected PMI to the basestation; and receiving a signal, transmitted from the base stationthrough a second beam determined based on the SRS switching signal andthe PMI.
 2. The method of claim 1, wherein the determining of theantenna subset is performed when the number of SRS switching resourcesallocated by the base station for the SRS switching signal is less thana number of reception antennas of the wireless communication device. 3.The method of claim 1, wherein the determining of the antenna subset isperformed when a number of RF chains of the wireless communicationdevice is less than a number of reception antennas of the wirelesscommunication device.
 4. The method of claim 1, further comprising:monitoring a gain value of the second beam; and determining a finalantenna subset based on the monitored gain value of the second beam. 5.The method of claim 4, further comprising calculating the gain value ofthe second beam by at least one of power of a received signal, a signalto noise ratio (SNR) of a received signal, frequency efficiency, anddecoding performance of a received signal.
 6. The method of claim 4,wherein the determining of the antenna subset comprises sequentiallydetermining each of a plurality of antenna subsets for each transmissionperiod of the SRS switching signal.
 7. The method of claim 4, furthercomprising determining the antenna subset as a final antenna subset whenthe gain value of the monitored second beam exceeds a predeterminedthreshold value.
 8. The method of claim 4, wherein the determining ofthe antenna subset comprises sequentially determining each of aplurality of antenna subsets based on a spatial correlation between theplurality of antennas.
 9. The method of claim 1, wherein the determiningof the antenna subset comprises determining an antenna subset based onreinforcement learning.
 10. The method of claim 4, further comprising:tracking the final antenna subset for each tracking period; and changingat least one antenna included in the antenna subset based on a trackingresult.
 11. The method of claim 1, wherein the determining of theantenna subset comprises determining the antenna subset based on atleast one of a signal to interference plus noise ratio (SINR) of thewireless communication device, a transmission/reception characteristicof an antenna, and a linearity of a transmission power amplifier. 12.The method of claim 1, wherein the selecting of the PMI comprisesselecting a PMI based on information on a weight applied to the CSI-RSreception channel.
 13. The method of claim 1, wherein the selecting ofthe PMI comprises selecting a PMI based on reinforcement learning.
 14. Awireless communication device comprising: a plurality of antennas; aradio-frequency integrated circuit (RFIC) including a switching networkconnected to the plurality of antennas, wherein the switching network isconfigured to transmit a sounding reference signal (SRS) switchingsignal to a base station through at least one antenna of an antennasubset of the plurality of antennas; and a processor configured to:determine the antenna subset; select a precoding matrix indicator (PMI)to be provided to the base station based on a channel stateinformation-reference signal (CSI-RS) transmitted from the base stationthrough a first beam; and process a signal transmitted from the basestation through a second beam determined based on the SRS switchingsignal and the PMI.
 15. The wireless communication device of claim 14,wherein, when a number of SRS switching resources allocated by the basestation for the SRS switching signal is less than a number of receptionantennas of the wireless communication device, the processor isconfigured to determine an antenna subset.
 16. The wirelesscommunication device of claim 14, wherein, when a number of radiofrequency (RF) chains of the wireless communication device is less thana number of reception antennas of the wireless communication device, theprocessor is configured to determine an antenna subset.
 17. The wirelesscommunication device of claim 14, wherein the processor is configured tomonitor a gain value of the second beam and determine a final antennasubset based on the monitored gain value of the second beam.
 18. Thewireless communication device of claim 14, wherein the processor isconfigured to sequentially determine each of a plurality of antennasubsets for each transmission 19-21. (canceled)
 22. A method ofoperating a base station communicating with a wireless communicationdevice including a plurality of antennas, the method comprising:receiving a sounding reference signal (SRS) switching signal transmittedthrough an antenna subset including at least one of the plurality ofantennas; estimating uplink channel information based on the SRSswitching signal; estimating downlink channel information based on theestimated uplink channel information; determining and forming a firstbeam based on the estimated downlink channel information, wherein achannel state information-reference signal (CSI-RS) is transmittedthrough the first beam; receiving a precoding matrix indicator (PMI)from the wireless communication device; determining and forming a secondbeam based on the received SRS switching signal and the received PMI,wherein a signal including data is transmitted through the second beam.23-25. (canceled)
 26. The method of claim 22, wherein a gain value ofthe second beam is monitored by the wireless communication device,wherein a final antenna subset is determined by the wirelesscommunication device based on the monitored gain value of the secondbeam. 27-31. (canceled)